Particle measuring device
Inventors
Kondo, Kaoru • BANDO, Kazuna • TABUCHI, Takuya • KONDO, Sota
Assignees
Publication Number
US-12265008-B2
Publication Date
2025-04-01
Expiration Date
2040-12-17
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Abstract
Provided is a particle measurement device in which irradiation light emitted by a light source is expanded by an expander in a shape satisfying the requirements of a diffractive optical element, converted into parallel light, and made to enter the diffractive optical element. The diffractive optical element shapes the irradiation light entering therein into a flat top beam in which the cross section in the focal position thereof has an elongate rectangle shape. The intensity distribution of light can be made substantially uniform in a detection area formed by the shaped irradiation light.
Core Innovation
The invention provides a particle measuring device that shapes irradiation light emitted by a light source into a flat top beam with a substantially oblong-and-sheet cross section at a focal position by using a diffractive optical element (DOE). This shaped irradiation light forms a detection region in a flow passage of a sample where particles pass, allowing scattered light from the particles to be detected and analyzed to obtain particle size.
The problem solved by this invention arises in conventional flow particle tracking (FPT) devices where irradiation light is typically a Gaussian beam. In such cases, the length of the particle passing direction in the detection region is not constant, causing variations in the number of times a particle can be captured depending on its passing position. This results in variations in particle size measurement accuracy and deteriorates particle size resolution. Furthermore, non-uniform energy density in the detection region reduces detection sensitivity and particle size resolution for light scattering-type particle measuring devices. Small detection regions can improve sensitivity but reduce effective flow rate, negatively impacting device performance.
To solve these problems, the invention employs a diffractive optical element to shape illumination into a uniform flat top beam of sheet-like shape extending in the depth-of-focus direction, thus forming a detection region with approximately uniform optical energy density. This enables high energy density and improved particle detection sensitivity over a wide range. The shaped irradiation light allows consistent capturing of particle movement and uniform scattered light intensity regardless of particle passage position, thereby improving the resolution of particle size measurements based on diffusion coefficient or scattered light intensity. The invention also introduces a beam expander to adjust the light source output to meet DOE requirements and multiple slit plates to remove high-order diffraction light, reducing noise and enhancing measurement accuracy.
Claims Coverage
The independent claims detail three main inventive features regarding the particle measuring device: beam shaping by a diffractive optical element, adjustment of irradiation light to meet DOE requirements, and separation of principal light beam from high-order diffraction light using slits.
Shaping illumination into a flat top beam with oblong-and-sheet cross section
A diffractive optical element is configured to shape light for irradiating particles into a flat top beam at a focal position with a substantially oblong-and-sheet cross section, which irradiates the sample flowing through a prescribed flow passage section to form a uniform detection region.
Adjustment of irradiation light to fit diffractive optical element requirements
A processor adjusts irradiation light emitted from the light source to have a diameter and beam divergence angle satisfying the diffractive optical element's requirements, ensuring optimal shaping of the irradiation light by the DOE.
Stepwise removal of high-order diffraction light via multiple slits
A slit or plurality of spaced slits separate the principal light beam from high-order diffraction light generated during the DOE shaping process by causing the principal light beam to pass while interrupting high-order diffraction light stepwise, thereby reducing noise in measurement.
Together, these inventive features enable formation of a sheet-shaped, uniform intensity detection region by shaping irradiation light using a DOE, optimizing the irradiation light shape for the DOE, and reducing measurement noise by removing stray high-order diffraction light, thereby improving particle size resolution and measurement accuracy.
Stated Advantages
Improves particle size resolution by forming a detection region with approximately uniform energy density using a sheet-shaped flat top beam.
Enables observation of light scattered from submicron-order particles over a wide range while maintaining a high effective flow rate.
Simplifies optical configuration compared to other beam shaping methods such as combinations of lenses.
Allows accurate shaping of irradiation light by adjusting its diameter and divergence angle before the diffractive optical element.
Reduces measurement noise effectively by removing high-order diffraction light with multiple slit plates, securing necessary measurement light while suppressing stray light.
Documented Applications
Use in flow particle tracking (FPT) devices to measure particle size by analyzing diffusion movement of particles via scattered light imaging.
Use in light scattering particle counters that determine particle sizes based on scattered light intensity signals.
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